This invention relates generally to a multilayer printed wiring board, either for surface mounting or through hole technology. More, particularly this invention relates to a multilayer printed wiring board which incorporates a high dielectric constant sheet material.
It will be appreciated that there is an ever increasing need for a reliable, flexible high dielectric material which may be used for a variety of applications in electronic circuitry design and manufacture. Presently, flexible high dielectric materials of this type are manufactured by mixing small particles (e.g. 1-3 microns) of a high dielectric constant material into a flexible polymeric matrix. Surprisingly, the resultant effective dielectric constant of the dielectric impregnated polymer is relatively low. For example, the dielectric constant of a Z5U BaTiO.sub.3 is in the range of 10,000 to 12,000. However, when such Barium Titanate is mixed with a flexible polymer such as polyimide, polyester, polyetherimide and like materials, the effective dielectric constant relizable is only on the order of 20 to 40 (depending on the loading ratio of the dielectric in the polymer).
It will be further appreciated that a need exists for a multilayer printed circuit board which provides power distribution free of the need for decoupling capacitors. This is because decoupling capacitors take up space on the surface of the board. This space can be used for integrated circuit chips or other functional components thereby increasing the amount of functional area on the board. Attempts have been made to construct a board which provides both power distribution and decoupling. One prior art attempt involves reducing the thickness of the dielectric layer between the voltage and ground planes. This attempt has proven unsatisfactory because of manufacturing problems. Because of the reduced thickness of the dielectric layer, pin holes are formed in it thereby resulting in electrical shorting of the circuit board. Also, the capacitance of the board varies with changes in the thickness of the dielectric layer. Another prior art board uses as a dielectric a suitable polymer filled with a high dielectric constant material such as barium titanate. The filled polymer is placed between the voltage and ground planes to create a capacitor effect. This prior art multilayer board has proven ineffective because the filled polymer has an effective dielectric constant of no more than about 80-100, which is too low for adequate results.